Corrugated feed horns improve the performance of circularly polarized parabolic antennas by providing nearly identical patterns for E and H planes. A corrugated feed horn with fins or lands much narrower than the grooves therebetween provides optimum RF performance. The fins and grooves alternate in an inner conical configuration.
At lower frequencies, feed horns can be made in a variety of ways, including machining. At SHF and EHF frequencies, the feed horns become small in diameter, and require thin fins and relatively deep grooves. This precludes machining because it is difficult and costly to machine the extremely thin fins, and because such machined thin fins commonly break off.
One method of making a feed horn with thin inner annular fins, is by electroforming. In this method, a conical mandrel is provided; and alternate layers of aluminum and copper washer-like flat annular rings of decreasing diameter are stacked along the mandrel. The outer periphery of the assembly is then electrocoated with copper to bond the layered rings, and the mandrel is removed. The assembly is then dipped in an etching acid solution to remove the aluminum and leave the copper rings as inner peripheral annular fins or lands with grooves therebetween. This method is subject to high tooling and piece-part costs.
Other methods include soldering and die casting. Die casting is subject to high tooling costs. Soldering is economical but weak because of poor tensile strength.